USMLE (Fach) / Respiratory (Lektion)

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• Neonatal respiratory distress syndrome Surfactant deficiency → ↑ surface tension → alveolar collapse ("ground-glass" appearance of lung fields). - Screening tests for fetal lung maturity: lecithin-sphingomyelin (L/S) ratio in amniotic ...
• Methemoglobin - oxidized form of Hb (Ferric, Fe3+) that does not bind O2 as readily, but has ↑ affinity for cyanide - may present with cyanosis and chocolate-colored blood - Induced methemoglobinemia (using nitrates, ...
• Carboxyhemoglobin - Form of Hb bound to CO instead of O2 - Causes ↓ oxygen-binding capacity with left shift in oxygen-hemoglobin dissociation curve- ↓ O2 unloading in tissues - CO bind competitively to Hb and with ...
• Oxygen-hemoglobin dissociation curve Sigmoidal shape due to positive cooperativity (ie, tetrameric Hb molecule can bind 4 O2 molecules and has higher affinity for each subsequent O2 molecule bound). Myoglobin is monomeric and thus does not ...
• Response to high altitude - ↓ atmospheric oxygen (PO2) → ↓ PaO2 → ↑ ventilation → ↓ PaCO2 → respiratory alkalosis → altitude sickness. - Chronic ↑ in ventilation. - ↑ erythropoietin → ↑ hematocrit ...
• Rhinosinusitis Obstruction of sinus drainage into nasal cavity → inflammation and pain - Typically affects maxillary sinuses, which drain against gravity due to ostia located superomedially - Most common acute cause ...
• Epistaxis = Nose bleed Most commonly in anterior segment of nostril (Kiesselbach plexus):- Anterior and posterior ethymoidal arteries- Superior labial artery- Greater palatine artery- Sphenopalatine artery - Life-threatening ...
• Head and neck cancer Mostly squamous cell carcinoma. Risk factors:- Tobacco- Alcohol- HPV-16 (oropharyngeal)- EBV (nasopharyngeal) Field cancerization: carcinogen damages wide mucosal area → multiple tumors that develop ...
• Deep venous thrombosis Blood clot within deep vein → swelling, redness, warmth, pain. Predisposed by Virchow triad (SHE):- Stasis (eg, post-op, long drive/flight)- Hypercoagulability (eg, defect in coagulation cascade proteins, ...
• Pulmonary emboli V/Q mismatch, hypoxemia, respiratory alkalosis. - Sudden-onset dyspnea- Pleuritic chest pain- Tachypnea- Tachycardia- Large emboli or saddle embolus may cause sudden death due to electromechanical dissociation. ...
• Obstructive lung diseases Obstruction of air flow → air trapping in lungs. Airways close prematurely at high lung volumes → ↑ RV, ↑ FRC, ↑ TLC (→ barrel chest). Pulmonary flow tests: ↓↓ FEV1, ↓ FVC → ↓ ...
• Chronic bronchitis ("blue bloater") Obstructive lung diseaseDiagnostic criteria: productive cough for >3 months per year for >2 consecutive years. Findings:- Wheezing, crackles- Cyanosis (hypoxemia due to shunting)- Dyspnea- CO2 retention ...
• Emphysema ("pink puffer") Obstructive lung diseaseEnlargement of air spaces, ↓ recoil, ↑ compliance, ↓ DLCO from destruction of alveolar walls.Imbalance of proteases and antiproteases → ↑ elastase activity → ↑ ...
• Asthma Obstructive lung diseaseHyperresponsive bronchi → reversible bronchoconstriction. Type I hypersensitivity reaction.Triggers: viral URIs, allergens, stress. Findings: - Cough, wheezing- Tachypnea, dyspnea, ...
• Bronchiectasis Obstructive lung diseaseChronic necrotizing infection of bronchi → permanently dilated airways. Findings:- Purulent sputum- Recurrent infections- Hemoptysis- Digital clubbing Associated with bronchial ...
• Asbestosis Pneumoconiosis Associated with shipbuilding, roofing, plumbing. (Asbestosis is from the roof, but affects the base) - "Ivory white," calcified, supradiaphragmatic and pleural plaques are pathognomonic. ...
• Silicosis Pneumoconiosis Associated with sandblasting, foundries, mines, glass production. - Macrophages respond to silica and release fibrogenic factors, leading to fibrosis.- It is thought that silica may disrupt ...
• Acute respiratory distress syndrome Alveolar insult → release of pro-inflamatory cytokines → neutrophil recruitment, activation, and release of toxic mediators (eg, reactive oxygen species, proteases, etc) → capillary endothelial ...
• Sleep apnea Repeated cessation of breathing >10 seconds during sleep → disrupted sleep → daytime somnolence. Diagnosis confirmed by sleep study. Normal PaO2 during the day.Nocturnal hypoxia → systemic/pulmonary ...
• Lung – physical findings Pleural effusion:- ↓ breath sounds- Dull percussion- ↓ fremitus Atelectasis (bronchial obstruction):- ↓ breath sounds- Dull percussion- ↓ fremitus- Tracheal deviation toward side of lesion ...
• Pleural effusions Excess accumulation of fluid between pleural layers → restricted lung expansion during inspiration. Can be treated with thoracocentesis to remove/reduce fluid. Transsudate: ↓ protein content.- Due ...
• Pneumothorax Accumulation of air in pleural space. Dyspnea, uneven chest expansion. Chest pain, ↓ tactile fremitus, hyperresonance, and diminished breath sounds. Primary sponteanous pneumothorax: - Due to rupture ...
• Pancoast tumor Carcinoma that occurs in the apex of lung. Compression of locoregional structures may cause array of findings:- Recurrent laryngeal nerve → hoarseness- Superior cervical ganglion (stellate ganglion) ...
• Superior vena cava syndrome An obstruction of the SVC that impairs blood drainage from the head. - Facial plethora- Jugular venous distension- Edema in upper extremities Commonly caused by malignancies (eg, mediastinal mass, Pancoast ...
• Small cell (oat cell) carcinoma Location: CentralUndifferentiated → very aggressive. - May produce ACTH (Cushing syndrome), SIADH, or antibodies against presynaptic Ca2+ channels (Lambert-Eaton myasthenic syndrome), or neurons (paraneoplastic ...
• Adenocarcinoma Location: Peripheral - Most common 1° lung cancer. - More common in women than men, most likely arise in nonsmokers.- Activating mutations include KRAS, EGFR, and ALK. - Associated with hypertorphic ...
• Squamous cell carcinoma Location: Central - Hilar mass arising from bronchus- Cavitation- Cigarettes- Hypercalcemia (produces PTHrP) Histology: Keratin pearls and intracellular bridges.
• Large cell carcinoma Location: PeripheralHighly anaplastic undifferentiated tumor; poor prognosis. - Strong association with smoking. Histology: Pleomorphic giant cells Treatment: Less responsive to chemotherapy; removed ...
• Lung development Occurs in five stages. Initial development includes development of lung bud from distal end of respiratory diverticulum during week 4. Embyronic (weeks 4-7): Lung bud → trachea → bronchial buds → ...
• Congenital lung malformations Pulmonary hypoplasia: Poorly developed bronchial tree with abnormal histology. Associated with congenital diaphragmatic hernia (usually left-sided), bilateral renal agenesis (Potter sequence). Bronchiogenic ...
• Club cells Nonciliated; low-columnar/cuboidal with secretory granules.  Located in bronchioles. Secrete component of surfactant; degrade toxins; act as reserve cells.
• Alveolar cell types Type I pneumocytes: - 97% of alveolar surfaces. Line the alveoli.- Squamous; thin for optimal gas diffusion. Type II pneumocytes:- Secrete surfactant from lamellar bodies → ↓ alveolar surface tension, ...
• Lung relations Right lung has 3 lobes, Left lung has 2 lobes and lingula. Relation of the pulmonary artery to the bronchus at each lung hilium is described by RALS - Right Anterior; Left Superior. Right lung is more ...
• Diaphragm structures Structures perforating diaphragm:- At T8: IVC, right phrenic nerve- At T10: Esophagus, vagus- At T12: Aorta, thoracic duct, azygos vein - Diaphragm is innervated by C3, 4, and 5 (phrenic nerve). - Pain ...
• Lung volumes Note: A capacity is a sum of ≥2 physiologic volumes. Inspiratory reserve volume: Air that can still be breathed in after normal inspiration, typically 3.3 L.Tidal volume: Air that moves into lung with ...
• Hemoglobin modifications Methemoglobin:- Oxidized form of Hb (ferric, Fe3+) that does not bind O2 as readily as Fe2+, but has ↑ affinity for cyanide.- Iron in Hb is normally in a reduced state (ferrous, Fe2+).- Nitrates (eg, ...
• Alveolar gas equation PAO2 = PIO2 - PaCO2/R ≈ 150 mmHg - PaCO2/0.8 PAO2 = alveolar PO2 (mmHg)PIO2 = PO2 in inspired air (mmHg)PaCO2 = arterial PCO2 (mmHg)R = respiratory quotient = CO2 produced/O2 consumed A-a gradient ...
• Oxygen deprivation Hypoxia (↓ O2 delivery to tissue)- ↓ cardiac output- Hypoxemia- Anemia- CO poisoning Hypoxemia (↓ PaO2)- Normal A-a gradient: High altitude, hypoventilation (eg, opioid use)- ↑ A-a gradient: ...
• Ventilation/perfusion mismatch Ideally, ventilation is matched to perfusion (ie, V/Q = 1) for adequate gas exchange. Lung zones:- V/Q at apex of lung = 3 (wasted ventilation)- V/Q at base of lung = 0.6 (wasted perfusion) Zone 1: PA ...
• Carbon dioxide transport CO2 is transported from tissues to lungs in 3 forms:1. HCO3- (70%).2. Carbaminohemoglobin or HbCO2 (21-25%). CO2 bound to Hb at N-terminus of globin (not heme). CO2 binding favors deoxygenated form (O2 ...
• Flow volume loops Obstructive lung volumes > normal (↑ TLC, ↑ FRC, ↑ RV); restrictive lung volumes < normal. In obstructive, FEV1 is more dramatically reduced compared with FVC --> decreased FEV1/FVC ratio. In ...
• Restrictive lung diseases Restricted lung expansion causes ↓ lung volumes (↓ FVC and TLC).Pulmonary flow tests: ↑ FEV/FVC ratio. - Patients present with short, shallow breaths. Types:Poor breathing mechanics (extrapulmonary, ...
• Inhalation injury and sequelae Complication of smoke inhalation from fires or other noxious substances. - Caused by heat, particulates (<1 µm diameter), or irritants (eg, NH3) → chemical tracheobronchitis, edema, pneumonia, ARDS.- ...
• Pneumoconiosis Coal workers' pneumoconiosis, silicosis and asbestosis → ↑ risk of cor pulmonale, cancer, and Caplan syndrome (rheumatoid arthritis and pneumoconiosis with intrapulmonary nodules). - Berylliosis, ...
• Coal workers' pneumoconiosis Prolonged coal dust exposure → macrophages laden with carbon → inflammation and fibrosis.- Also known as black lung disease. - ↑ risk for Caplan syndrome (rheumatoid arthritis and pneumoconioses ...
• Mesothelioma Malignancy of the pleura associated with asbestosis. Clinical findings:- Dyspnea and nonpleuritic chest pain- Fever, sweats, weight loss May result in hemorrhagic pleural effusion (exsudative), pleural ...
• Pulmonary hypertension Normal mean pulmonary artery pressure = 10-14 mmHg.Pulmonary hypertension ≥25 mmHg at rest.- Results in arteriosclerosis, medial hypertrophy, intimal fibrosis of pulmonary arteries, plexiform lesions. ...
• Pneumonia Lobar:- S pneumoniae most frequently, also Legionella, Klebsiella.- Intra-alveolar exudate → consolidation; may involve entire lobe or the whole lung. Bronchopnemonia: - S pneumoniae, S aureus, H ...
• Natural history of lobar pneumonia Congestion:- Days 1-2- Red-purple, partial consolidation of parenchyma- Exudate with mostly bacteria Red hepatization:- Days 3-4- Red-brown, consolidated- Exudate with fibrin, bacteria, RBCs, WBCs Gray ...
• Lung abscess Localized collection of pus within parenchyma. Caused by aspiration of oropharyngeal contents (especially in patients predisposed to loss of consciousness [eg, alcoholics, epileptics]), or bronchial obstruction ...

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